The present invention is directed to equipment and process for treatment of exhaust gas from internal combustion engines, particularly the injection of a treatment liquid upstream of a selective catalytic reaction (SCR) converter.
U.S. Pat. No. 5,976,475, “Reducing NOx Emissions from an Engine by Temperature-Controlled Urea Injection for Selective Catalytic Reduction”, describes a process in which a spray of urea solution is injected into the exhaust gas stream upstream of an SCR converter. The exhaust pipe or conduit becomes quite hot, and the ambient air surrounding the exhaust pipe is likewise quite hot. The urea solution must remain below the transition temperature of the urea solution, to avoid the formation of ammonia. The required temperature control proposed in said patent is to maintain circulation of the urea solution between the source and the injector, whether or not the injector is discharging into the exhaust. The continuous flow means that a given unit of urea solution volume that leaves the source at about 100 deg. C. is exposed to the hot injector environment for only a brief period, so it does not rise to the critical temperature of about 135 deg. C.
Publication No. US2005/0235632, “Methods and Apparatus for Injecting Atomized Fluid”, discloses one such injector configuration, in which treatment liquid is continuously recirculated to and from a source, while a standing swirl is maintained in the lower portion of the injector bore, above the valve seat, such that upon a valve actuation signal the valve lifts from the seat and the liquid in the standing swirl passes through the discharge orifice as an atomized swirl, into the exhaust stream of the pipe.